1. Field of the Invention
This invention relates to nonwoven fabrics made by thermally bonding fibrous webs made from certain types of multiconstituent fibers, and to laminates incorporating said fabrics. Thermal bonding of the nonwoven fabrics may be accomplished by calender or `through air` techniques or ultrasonically. The multiconstituent fibrous webs may contain other fibers in addition to the thermoplastic multiconstituent fibers. The nonwoven fabrics produced according to the present invention may be optimized as to softness and strength characteristics.
2. Description of the Prior Art
Structured multicomponent fibers--made by coextrusion of different polymers in a variety of structured configurations--have long been well-known. Some relevant references are: Davies (U.S. Pat. No. 3,595,731), Gerlach (U.S. Pat. No. 4,361,609), Kiriyama (U.S. Pat. No. 4,568,506), and Uchikawa (U.S. Pat. No. 4,770,925).
A few references cite fibers and nonwoven fabrics made from polymer blends wherein the dominant continuous phase is lower melting than is the dispersed noncontinuous phase; see Kubo (European Patent Application No. 0277707), Wincklhofer (U.S. Pat. No. 3,620,892) and Vassilatos (U.S. Pat. No. 4,632,861). By definition, to thermally bond such fibers, portions of the continuous fiber phase are raised to temperatures where partial molecular relaxation of the continuous lower melting phase occurs. Relaxation occurs not only at the bond sight proper but also in the fiber region surrounding the bond sight which is responsible for distributing a load or strain throughout the bonded fiber network. Although thermally-bonded nonwoven fabrics can be made from these materials, strength is compromised.
Some instances are also known wherein blends of different polymers are extruded from the orifices of spinnerets in order to make fibers containing "free form" microfibrils which can then be separated from the matrix polymer: Breen (U.S. Pat. No. 3,382,305), Twilley (U.S. Pat. No. 3,369,057), and Allan (U.S. patent application Ser. No. 07/220,203), now abandoned.
Finally, Graham (U.S. Pat. No. 4,769,279) refers to meltblown fibers and fabrics made from blends of ethylene/acrylic copolymer with a second fiber-forming polymer such as a polyvinyl, a polyamide, and a polyolefin. Graham does not disclose thermally-bonded nonwoven fabrics from engineered fibers, however. Furthermore, the Graham disclosure is limited to blends based upon low viscosity ethylene/acrylic copolymers.